A five-year study of two intensively managed pasture-crop rotations has yielded new insights into pasture and rotation dynamics. Diversity may, here as elsewhere, be the key to stability.
Results also showed that more focused management prior to cropping, particularly in relation to the method of weed control, has a substantial impact on the size and persistence of pasture legume seed banks.
Frequent use of spraytopping led to a rapid decline in the legume seed bank and resulted in the need for resowing. By comparison, strategic use of grass-selective herbicides and insecticides built up legume seed banks.
Where and why
Two large plots in the central wheatbelt of WA (Jennacubbine and Cunderdin) formed part of a GRDC-supported investigation into what factors of pasture productivity limit cereal crop yield. The larger aim was to enhance the contribution of the pasture phase of rotation to subsequent cereal yields, grain quality and overall farm profitability.
Other results showed that although focusing management inputs lifted legume seed banks, high germinable seed pools did not always flow through to greater legume biomass and greater nitrogen supply to cereals.
At Cunderdin this result arose through a major fungal outbreak in the medic pasture. At Jennacubbine it was caused by poor establishment of subterranean clover in three consecutive years with late false breaks.
Poor legume stability due to factors beyond the control of farmers is a big problem. False breaks occur as frequently as once every two years in some medium-rainfall areas of southern Australia.
The collaborative venture brought together AGWEST and CSIRO expertise from different fields with support work on pasture ecology, animal nutrition, insect ecology, nitrogen transformation and leaching studies.
Research results point to...
Increasing the diversity of pasture species, together with good management to maintain high legume seed banks, may be the best option for improving the stability of the legume and hence the reliability with which benefits of a pasture phase are expressed in subsequent crops. A mix of cultivars within a species is unlikely to provide enough diversity.
Many new legume species are now available to farmers including Arrowleaf, balansa, crimson and Persian clovers, French and yellow serradella, and biserrula. Such species have a diversity of dormancy release patterns, levels of hard seed, seed size, seedling drought tolerance and likely resistance to disease and insect threats.
Evaluation of mixed sowings
Over the next five years the Pasture Management Group at AGWEST will involve farmers in the on-farm evaluation of species mixtures.
Contact: Dr Clinton Revell 08 9690 2117 or Mr David Ferris 08 9380 7980